To be frank, your daughter's behavior seems very normal for the age. Her upset is well within the norms for her age and there does not seem to be any reason for alarm. Now, the comments about choking and killing are unusual, and they invite some casual questions about what she was thinking (e.g., What made you think about that? What would happen if someone did that?).
This may be her way of recieving attention. She knows that her harsh statements will cause you alarm. Even though she is four she can be felling left out, less important than the twins. She does not have the correct vocabulary to express her frustration, anger, sadness. She may have also heard others say, I just want to choke someone or something similar. Children pick up on these things. I think it is important to try and talk with her to find out what she is feeling and give her the words to express these things. Also you may try to have just you and her time. Maybe go and get a minicure or set time at home for just you and her if possible to do her nails or something she likes to do together. Also telling her those things are not acceptable to say and having consequences. She may just need more reassurance that she is still special.